Into the Garden: Mulch protects tree roots over winter

CHARLESTON, W.Va. -- The late-October snowfall caught a lot of us by surprise. I had planned to rake and blow leaves, mulch the beds, etc., but now I'm playing catch-up. The Morton Arboretum recommends mulching around trees to protect against damage from the cold. Since we've lost so many trees to the storms of 2012, I'm doing my best to keep the ones that are left.

When used properly, mulch stabilizes soil temperatures, helping to prevent root injury and stress that can occur during freeze-thaw cycles.

If you didn't mulch your trees this summer, there's still time to apply it.

Mulching plants is functional and decorative. Mulch typically is an organic material spread on the soil surface to protect roots from heat, cold and drought, and to provide nutrients to plants as it decomposes. Once you have chosen the right plant for a given site, and followed the proper planting procedures, you should mulch the plant and create a stable environment for root growth.

Several factors should be considered when choosing mulch. Medium-textured mulch is best. Fine particles tend to pack down and retain moisture, which then evaporates before reaching plant roots. Coarse-textured materials may be too porous to hold adequate amounts of water.

Organic mulch provides nutrient-rich humus as it decomposes. This also improves soil structure.

Types of organic mulch

Grass clippings. Dry or compost before using. Mix with other materials to increase porosity and reduce matting. A source for some nitrogen but also higher alkalinity, which may compromise nutrition.

Hardwood bark. Pine bark or shredded bark can be purchased as bags of small or large chips. Long-lasting.

Hardwood chips. Readily available and often free from municipal sources. If chips are not composted, apply a nitrogen fertilizer at a rate of 1/2 pound per 100 square feet of chips.

Composted leaf litter (leaf mold). A good source of nutrients, but may increase weeds if not thoroughly composted.

Animal manure. A good source of nutrients. Compost before applying or plant damage (burn) may result because of high salt content. Ideally, should be mixed with a coarse-textured material.

Mushroom compost. A good source of nutrients when mixed with other materials. Source of large amounts of alkalinity and sometimes salts.

Peat moss. Compacts easily due to fine texture and dries out quickly. Not recommended as a top dressing because water will not penetrate when dry.

Pine boughs. This is a good covering for perennials in the winter.

Pine needles. Not widely available and should be mixed with other materials unless soil acidity is desired.

Shredded leaves. Leaves are variable in texture and can be collected and shredded at home. Mix into the soil in the fall and allow to break down naturally during the winter for improved soil quality.

Straw. Coarse-textured so it persists a long time, but can blow away easily unless mixed with other materials. Generally not suitable as a landscape mulch, but provides winter protection and cover for grass seed.

Applying mulch

Spread mulch under trees, shrubs and throughout planting beds to a recommended depth of 3 to 4 inches for medium- to coarse-textured materials.

Pull mulch away from the bases of tree and shrub trunks creating a doughnut hole. Do not pile it up against the trunk ("volcano mulching"). Excessive mulch on the trunk causes moisture to build up, creating ideal conditions for insect pests, diseases and decay.

Ideally, the mulched area around a tree should extend to the drip line of the branches, or at least cover a 4- to 5-foot diameter area around the trunk. The larger the mulched area, the more beneficial.

Check mulch depth annually and replenish as necessary.

Mulch provides an insulation layer. Mulched soils are warmer in winter and cooler in summer than bare soils. Roots are protected from temperature extremes, creating less freezing and thawing of the soil in winter, which can heave and injure plants.